The present invention relates to an ink cartridge used as an ink supplying source of an ink jet printer. In further detail, the invention relates to an ink cartridge capable of supplying ink with an ink supplying needle at an ink jet printer side inserted into a needle insertion hole formed on a gasket attached to an ink outlet port when the same ink cartridge is mounted in an ink jet printer.
In this type of ink cartridge, for example, as disclosed in Japanese Patent Publication Nos. 2001-113723A and 2002-192739A, an annular projection which protrudes outward from the circumference of a gasket press-fitted to an ink outlet port is formed at the outer circumferential face thereof, and sealing of the gasket is secured. That is, if a gasket is press-fitted to the ink outlet port, the annular projection is forcibly crushed, wherein spacing between the inner circumferential face of the ink outlet port and the outer circumferential face of the gasket is sealed. As a result, air is prevented from invading an ink reservoir in the ink cartridge from outside, passing through the spacing between the outer circumferential face of the gasket and the inner circumferential face of the ink outlet port. Also, air bubbles are prevented from flowing out from the ink reservoir.
The gasket attached to the ink outlet port is formed of a rubber material such as silicone rubber, chloroprene rubber, butyl rubber, etc., or a resilient material such as elastomer resin, etc. These rubber materials and elastomer resin deteriorate over time, and plastic deformation thereof becomes worse. Therefore, the sealing property of a gasket is weakened by chronological deterioration, wherein there is an anxiety that, by a force acting on the gasket when attaching and detaching an ink cartridge, air invades inwardly from outside through spacing between the outer circumferential face of the gasket and the inner circumferential face of the ink outlet port, or air bubbles are flown out from inside to outside. Also, where an ink cartridge is stored or where an ink cartridge remains attached in a printer for a long time period, there is a concern that air gradually invades between the outer circumferential face of the gasket and the inner circumferential face of the ink outlet port, so that air bubbles are deposited at the ink outlet port. Accordingly, air bubbles may be supplied to the ink jet head side of an ink jet printer together with ink, resulting in faulty discharge of ink liquid droplets and an inability to discharge, wherein a deterioration in printing quality results.